Comprehensive characterization of pathogenic synovial fluid extracellular vesicles from knee osteoarthritis

• Published in: Clinical immunology (Orlando, Fla.) Fla.), 2023-12, Vol.257, p.109812-109812, Article 109812
• Main Authors: Zhang, Xin, Ma, Sisi, Naz, Syeda Iffat, Jain, Vaibhav, Soderblom, Erik J., Aliferis, Constantin, Kraus, Virginia Byers
• Format: Article
• Language: English
• Subjects: Biomarkers - metabolism; Chondrocytes; Extracellular vesicles; Extracellular Vesicles - metabolism; Humans; Immune cells; Innate immune system; Knee osteoarthritis; Osteoarthritis, Knee - metabolism; Peptides - metabolism; Surface markers; Synovial fluid; Synovial Fluid - metabolism
• ISSN: 1521-6616; 1521-7035
• DOI: 10.1016/j.clim.2023.109812

Synovial fluid (SF) extracellular vesicles (EVs) play a pathogenic role in osteoarthritis (OA). However, the surface markers, cell and tissue origins, and effectors of these EVs are largely unknown. We found that SF EVs contained 692 peptides that were positively associated with knee radiographic OA severity; 57.4% of these pathogenic peptides were from 46 proteins of the immune system, predominantly the innate immune system. CSPG4, BGN, NRP1, and CD109 are the major surface markers of pathogenic SF EVs. Genes encoding surface marker CSPG4 and CD109 were highly expressed by chondrocytes from damaged cartilage, while VISG4, MARCO, CD163 and NRP1 were enriched in the synovial immune cells. The frequency of CSPG4+ and VSIG4+ EV subpopulations in OA SF was high. We conclude that pathogenic SF EVs carry knee OA severity-associated proteins and specific surface markers, which could be developed as a new source of diagnostic biomarkers or therapeutic targets in OA. We hypothesize that pathogenic SF EVs can be identified by their OA severity-associated protein cargo; these could in future enable targeting to develop new OA biomarkers and therapeutics. To test our hypothesis, first, we identified knee rOA severity-associated peptides in SF and plasma EVs (termed EV peptidesrOA-Pos); second, we identified peptides that were more abundant in SF EVs than matched plasma EVs (termed EV peptidesSF>PL); third, we identified surface markers comprised of EV peptidesSF>PL that were highly associated with SF EV peptidesrOA-Pos; fourth, we validated expression of genes encoding these surface markers in end-stage knee OA joint tissue cells; last, we validated the presence of EV subpopulations carrying these surface markers in end-stage knee OA SF. Graph was created with BioRender.com. [Display omitted] •To our knowledge, this is the first study reporting a comprehensive non-targeted proteomic analysis of EVs from matched plasma and SF from knee OA patients, thereby identifying an array of surface markers of pathogenic SF EVs with determination of their OA joint tissue of origin.•The results of this study firmly support EVs, predominantly SF EVs, as potential diagnostic biomarkers and/or therapeutic targets of OA. Their potential involvement in the pathogenesis of knee OA is based on the demonstrated pathogenic roles of proteins identified as EV peptidesrOA-Pos that were positively associated with knee rOA severity, and more abundant in SF EVs than plasma EVs (SF EV peptidesSF>P